“You're enjoying your day, everything's going your way, then along comes Debbie Downer, always there to tell you 'bout a new disease, a car accident or killer bees You'll beg her to spare you, 'Debbie, Please!' But you can't stop Debbie Downer!”

So goes the theme song of Saturday Night Live’s famous party-pooper, as played by Rachel Dratch, in a role that will now be assumed, much to his regret, by Benjamin Netanyahu. The Israeli prime minister arrives in New York on Sunday morning with overweight baggage full of stern warnings, dire predictions and apocalyptic prophecies all aimed at throwing cold water on the Administration’s victory celebrations.

Because there’s no denying that from President Obama’s point of view, it has been a weekend of unprecedented diplomatic triumphs. His historic phone call with Iranian President Rohani, followed a few hours later by the unanimous Security Council endorsement of US-Russian plan to rid Syria of its chemical weapons, were like back-to-back walk-off grand slams in a crucial baseball doubleheader.

Even if neither of these developments could have been foreseen a month ago, as a senior Administration official admitted on Friday, there was no denying the loud cheers of self-congratulation that emanated from Washington in their wake.

Many people may believe that Obama has been more lucky than clever, but the Administration’s narrative of developments in recent weeks was nonetheless unequivocal. The president’s threat to attack Syria was the sine qua non that led to Friday’s rare Security Council consensus, just as Obama’s forceful leadership of the international campaign to impose sanctions on Iran was the trigger for Rohani’s recent election, his trip to the UN and the new opening that has been created to resolving the outstanding nuclear dispute with Tehran.

So what may seem to many Israelis as a dangerous trip in la la land is perceived in the White House as a potential affirmation of central tenets of the basic world view that Obama brought with him to the White House five years ago: judicious use of America’s military power and diplomatic clout to enlist the international community against rogue regimes; resolute prevention of proliferation of weapons of mass destruction; reengagement in and rebuilding of multilateral bodies such as the United Nations, the International Atomic Energy Agency and the Organization for the Prevention of Chemical Weapons.

These diplomatic breakthroughs are doubly prominent against the backdrop of the ongoing paralysis in Washington and the Gog and Magoggian wars in Congress pitting the Ted Cruz – Tea Party wing of the Republican Party against the rest of the world. The looming showdown over Federal shutdown and the Affordable Care Act not only threaten to deprive Netanyahu of much of the media attention he would otherwise have garnered, it also depletes his reserves of usually-reliable allies against what he surely views as the Administration’s naïve complacency towards Damascus and Tehran.

With the Republican Party consumed by its own internal convulsions, it is small wonder that many of the usual voices warning against “selling out” Israel or comparing Munich 1938 to Tehran or Geneva 2013 fell unusually silent throughout the recent days of Rohani’s courtship of America. Politicians and pundits who would normally echo much of the arguments that Netanyahu is bound to make were more preoccupied, with the potentially existential threat to the Republican Party rather than the one said to be confronting Israel.

The volume of objections to Rohani’s message voiced by Jewish leaders and organizations was also uncharacteristically low, for a variety of reasons, including, of course, the Succoth festival. But Jewish groups may also have felt inhibited because of Rohani’s deft if disingenuous deflection of the Holocaust-denial controversy and out of fear of appearing to be reflexively hawkish, following their support for Obama’s now abandoned militancy in Syria as well.

Obama and other Administration officials will doubtlessly do their best to calm Netanyahu’s fears and to carefully his reservations and recommendations in private meetings, as well as to show their empathy and backing in public. With the American media, swept away at times by Rohani’s charm and promises of new beginnings, Netanyahu will have to be at his public relations best.

But when he comes to the United Nations on Tuesday to serve as the last speaker at this year’s General Assembly, Netanyahu will discover that the party’s over, the barricades have been dismantled, most of the foreign leaders have left town, the journalists have turned their attention elsewhere and most observers have concluded that all in all, it was a great success.

Only the future can tell whether Netanyahu’s warnings will be borne out or refuted, but in the meantime he runs the risk of being portrayed as a perennial party-pooper and a chronic Cassandra. At a time when Washington and the rest of the world prefer to be sunny and optimistic Netanyahu – to cite another song made famous by Barbra Streisand in “Funny Girl” and Lea Michele in “Glee” – is coming to town to rain on their parade.

Haaretz.com, the online edition of Haaretz Newspaper in Israel, and analysis from Israel and the Middle East. Haaretz.com provides extensive and in-depth coverage of Israel, the Jewish World and the Middle East, including defense, diplomacy, the Arab-Israeli conflict, the peace process, Israeli politics, Jerusalem affairs, international relations, Iran, Iraq, Syria, Lebanon, the Palestinian Authority, the West Bank and the Gaza Strip, the Israeli business world and Jewish life in Israel and the Diaspora.